Optical glass having anomalous partial dispersion

ABSTRACT

NOVEL GERMANIUM-CONTAINING OPTICAL GLASS COMPOSITIONS HAVING ANOMALOUS PARTIAL DISPERSION AND IMPROVED CHEMICAL PROPERTIES CONTAINING GLASS BATCH CONSTITUENTS RANGING IN WEIGHT PERCENT: 37-50% OF GLASS FORMERS SELECTED FROM THE GROUP OF METAL OXIDES CONSISTING OF SIO2, B2O3, AND GEO2; AT LEAST 6% OF AN ALKALI METAL OXIDE, AT LEAST 2% OF AN OXIDE SELECTED FROM THE GROUP CONSISTING OF ZNO AND CDO, UP TO 13% OF AN OXIDE SELECTED FROM THE GROUP CONSISTING OF AL2O3 AND LA2O3 3-8% OF ZRO2 AND 25-42% OF AN OXIDE SELECTED FROM THE GROUP CONSISTING OF TA2O5 AND/OR WO3 OR NB2O5 WITH AT LEAST 20% OF THE OXIDE OF TANTALUM BEING PRESENT. THE REFRACTIVE INDICES (NE) OF SUCH GLASSES RANGE APPROXIMATELY FROM 1.646 TO 1.733 WHILE THE ABBE VALUES (VE) RANGE BETWEEN 44.8 AND 37.1 AND THE PARTIAL DISPERSIONS ($VE) ARE FROM -3.0 TO -6.4.

Sept. 12, 1972 H, BROMER EIAL 3,690,905

OPTICAL GLASS HAVING ANOMALOUS PARTIAL DISPERSION Filed May 20, 1971 (We/9hr "/o) l N VE N TOR$ 5W2 RUE/16R AL- United States Patent 3,690,905 OPTICAL GLASS HAVING ANOMALOUS PARTIAL DISPERSION Heinz Bromer, Hermannstein, Norbert Meinert and Johann Spincic, Wetzlar, and Hans Staaden, Stockhausen, Germany, assignors to Ernst Leitz G.m.b.H.,

Wetzlar, Germany Filed May 20, 1971, Ser. No. 145,321 Claims priority, application Germany, May 22, 1970, P 20 24 912.1 Int. Cl. C03c 3/08, 3/33, 3/00 US. Cl. 106-47 Q 2 Claims ABSTRACT OF THE DISCLOSURE Novel germanium-containing optical glass compositions having anomalous partial dispersion and improved chemical properties containing glass batch constituents ranging in weight percent: 37-50% of glass formers selected from the group of metal oxides consisting of SiO B 0 and Geo at least 6% of an alkali metal oxide, at least 2% of an oxide selected from the group consisting of ZnO and CdO, up to 13% of an oxide selected from the group consisting of A1 0 and 1321 0 38% of ZrO and 25-42% of an oxide selected from the group consisting of Ta O and/ or W0 or Nb Og with at least 20% of the oxide of tantalum being present. The refractive indices (7 of such glasses range approximately from 1.646 to 1.733 while the Abbe values (w range between 44.8 and 37.1 and the partial dispersions (Av are from 3.0 to -6..4.

BACKGROUND OF I l-IE INVENTION In the US. Pat. 3,529,980 optical crown glasses are disclosed which are molten from a batch composition containing as the glass former only SiO and B 0 The glasses have indices of refraction ranging between 1.54 and 1.64 with an anomalous negative partial dispersion (Av between 3 and 14. However, optical glasses having about the same anomalous partial dispersion but in combination with a considerably higher index of refraction have often been required by the lens designers. It is therefore an object of the present invention to provide such glasses with a high index of refraction.

SUMMARY OF THE INVENTION According to the invention the above stated object is attained by adding a considerable amount of germanium dioxide (Geo to the batch composition as a glass former.

As a matter of fact, Geo is already known to have glass forming properties, and glasses consisting only of Ge0 have already been manufactured because of their specific optical properties in the range of the infrared light.

Further, for melting particular infrared light transmitting glasses Si0 has already been replaced partially or totally by GeO However, if the optical glasses are required to have certain well defined optical properties in the range of the visible light, as for example a certain index of refraction (1 Abbe number (w and an anomalous partial dispersion (Av and further, if the glasses are to be reproducible and to be molten without difiiculties, then the glasses must be molten from certain specific batch compositions from which glasses are obtained which will be resistant to chemical influences.

According to the invention such glasses will be obtained from batch compositions which consist essentially of the following constituents given in percent by weight:

(a) 37-50% of the glass formers SiO B 0 and GeO- of which SiO- is present in an amount of at least 8%, B 0 is present in an amount of at least 12% and GeO is present in an amount of at least 10%;

(b) at least 6% of the alkali metal oxides U 0 and/ or Na O with the ratio of the weight of U 0 and Na O being approximately 6 in cases where both U 0 and Na O are present;

(c) at least 2% of the oxides of elements selected from the group consisting of zinc and cadmium;

(d) 043% of the oxides of elements selected from the group consisting of aluminum and lanthanum;

(e) 3-8% of zirconium dioxide ZrO (f) 25-42% of the oxide of tantalum or of the oxides of the elements selected from a group consisting of tantalum and tungsten and niobium respectively, with at least 20% of the oxide of tantalum Ta O being present.

Within the described ranges preferred glasses are molten from a batch composition consisting essentially of:

(a) 37-50% of the glass formers SiO B 0 and GeO of which SiO is at least 8%, B 0 is at least 14% and GeO is 14%;

(b) 68% of the oxides of the alkali metals U 0 and/ or Na O with the ratio of the weight of Li O and Na O being approximately -6 in cases where both U 0 and Na O are present;

(0) 3.1% of zinc oxide ZnO;

(d) up to 13% of the oxides of the elements selected from a group consisting of aluminum and lanthanum;

(e) 3-8% of the zirconium dioxide 210 (f) 2542% of the oxide of tantalum or of the oxides of the elements selected from a group consisting of tantalum and tungsten with at least 20% of the oxide of tantalum Ta O' being present.

BRIEF DESCRIPTION OF THE DRAWING The figure represents a ternary phase diagram of the glass formers SiO B 0 and GeO wherein the amount of each ingredient is given in percent by weight. For the purpose of this diagram the total amount of the glass formers was made to equal Le.

and the calculated percent by weight of these glass formers is given in the Table 1 below:

DESCRIPTION OF THE PREFERRED EMBODIMENTS The results of a number of glass melts are shown in the following table which also gives for each molten glass the index of refraction 7 the Abbe number w and the partial dispersion Av By these melts it is proven that, in the sense of the invention, Geo -containing glasses can be molten which have a considerably higher index of refraction than those disclosed in the US. Pat. 3,529,980. The lens designer can, thus, select the glass types from a wider range of specific glasses.

from the group consisting of zinc and cadmium;

(d) to 13% of the oxides of an element selected from the group consisting of aluminum and Ianthanum;

(e) 3% to 8% of zirconium dioxide ZrO and (f) 25% to 42% of the oxides of an element selected TABLE 2 (In percent by weight) Melt number 1 2 3 4 5 6 7 8 9 10 A melt is completed by filling l-2 kg. of the mixed from the group consisting of tantalum, tungsten, and batch particles into a platinum crucible and melting the niobium, with at least 20% of the oxide of tantalum constituents at 1300 C. The temperature is then raised Ta O being present in said glass composition. to 1400 C. and the melt is homogenized by continuous 2. An optical glass composition as claimed in claim 1, stirring over a period of one hour. Thereafter, the term wherein the glass batch constituents of said glass compoperature is lowered to 1250 C. while still stirring and sition are present therein in the following weight percent further to 800 C. where the molten material is cast into ranges: a preheated mold. (a) 37% to 50% of the glass formers silicon dioxide The invented glasses are easy to melt bubble-free and SiO boron trioxide B 0 and germanium dioxide without streaks. They are highly resistant against atmos- 'GeO of which silicon dioxide is present in an pheric influences. amount of at least 8%, boron trioxide is present in The seven points recorded in the diagram correspond to an amount of at least 14%, and germanium dioxide the melt examples described in the Tables 1 and 2. is present in an amount of 14%;

What is claimed is: (b) 6% to 8% of the alkali metal oxides selected 1. An optical glass composition consisting essentially from the group consisting of lithium oxide Li O, of silicon dioxide SiO boron trioxide B 0 germanium sodium oxide Na O, and mixtures thereof, with the dioxide GeO alkali metal oxides, zirconium dioxide ratio of the weights of lithium oxide Li O and ZrO and the oxides of tantalum, tungsten, and niobium, sodium oxide Na O being about 6 in cases where said glass composition having a refractive index (w beboth lithium oxide and sodium oxide are present; tween about 1.64 and about 1.74 and an Abbe value (w (c) 3.1% of zinc oxide ZnO; ranging between about 37.1 and about 44.8, and a nega- (d) up to 13% of th oxide of an element selected tive partial dispersion value (Ar ranging between about from the group consisting of aluminum and lan- 3.0 and about 6.4 the glass batch constituents of said thanum; glass composition being present therein in the following 3% to 8% of irconium dioxide ZrO and weight percent ranges: (f) 25 to 42% of the oxides of an element selected 37% t0 0f the glass formers silicon dioxide 50 from the group consisting of tantalum and tungsten SiO boron trioxide B 0 and germanium dioxide whereby at least 20% of the oxide of tantalum T8205 GeO of which silicon dioxide is present in an are present in said glass composition. amount of at least 8%, boron trioxide is present in an amount of at least 12%, and germanium dioxide f r n s Cited is present in an amount of at least 10%; 0 UNITED STATES PATENTS (b) at least 6% Of the alkali 1116131 oxides selected 3 529 9 0 9 1970 a et 1 1156 47 Q from the group consisting of lithium oxide Li O, sodium oxide Na O, and mixtures thereof, with the JAMES E. POER, Primary Examiner ratio of the weights of lithium oxide and sodium M L. BELL Assistant Examiner oxide being about 6 in cases where both lithium oxide and sodium oxide are present; (c) at least 2% of the oxides of an element selected US. Cl. X.R. 10654 mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIUN Patent No. 3 5 Dated September 12, 1972 lnventofls) HEINZ BROEMER, NORBERT MEINERT, JOHANN SPINCIC It is certified that error appeers in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Drawing page, line 1; column l, line 4: The name of the inventor "Bromer" should be changed to, Broemer -7 column 1, line 27, line 38, line 62 column 2, line 66;

Table 2; column 3 line 43: 42 should rad n Signed and sealed this 3rd day of April 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. I ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

